One of the most common and persuasive arguments against gun control is that guns offer a means with which good guys can protect themselves from bad guys.
In practice, unfortunately, the guns that good guys own to protect themselves from bad guys too often end up killing the good guys' kids or wives or the good guys themselves (either via suicide, accident, or, in some cases, because they're grabbed by the bad guys and used against the good guys). Or, as in the case of Florida teen Trayvon Martin, the guns kill people who the good guys think are bad guys but who aren't actually bad guys.
But, sometimes, the guns actually do what gun-control opponents say they do.